Behavioral Indexes of Thermal Nociceptive Sensitivity in Rats after Melatonin Administration

We studied the effect of melatonin (10 mg/kg intraperitoneally) on behavioral indexes reflecting changes in nociceptive sensitivity of rats in response to thermal stimulation in the hot plate test. Administration of melatonin to animals suppressed the perceptual component of nociception, which was manifested in an increase in the perception threshold of noxious thermal stimulus. In the follow-up period, exogenous melatonin contributed to a decrease in the latency of avoidance reactions and enhanced the behavior of escaping the thermal nociceptive stimulation. Our results suggest that the involvement of melatonin in goal-directed behavior of mammals during nociceptive treatment is related to an increase in orientation and exploratory activity, facilitation of memory storage, and improvement of memory retrieval for environmental signals, action program, and reinforcing effect of avoiding the painful stimulus.